Method of liquefying gas



March 5, 1957 w. MORRISON 2,783,624

METHOD OF LIQUEFYING GAS Filed Sept. 29, 1951 '17? 0622 for Q fly/(mil Jfvrrzlsow United States Patent METHOD OF LIQUEFYING GAS Willard L. Morrison, Lake Forest, 111., assignor, by mesue assignments, to Constock Liquid Methane Corporation, a corporation of Delaware Application September 29, 1951, Serial No. 248,973 2 Claims. c1. 62-175) "a residual refractory gas that remains after the refinery has removed the liquids such as gasoline, kerosene, fuel oil lubes and the like and after the so-called liquid petroleum gases such as propane and the like have been extracted.

Methane must be lowered in temperature to approximately l15.8 degrees F. before it can be liquefied. Above that temperature no matter how great pressures are applied, it will not liquefy. The gases .of higher boiling point can be compressed or liquefied and stored and shipped in the usual type of commercial gas bottles or gas tanks though they require under ordinary circumstances bottles or tanks of great weight and strength.

The problem which I propose to solve while in the main similar to problems that have been solved in the past with less satisfaction, is a diiferent one in that I propose the storage and shipment of very much larger quantities of this refractory methane gas.

In general, I propose to liquefy this gas by reducing its temperature and raising its pressure to a point below the critical temperature and above the critical pressure, then this liquid gas will be reduced'in pressure to somewhere in the neighborhood of atomspheric. Its temperature as a result of such pressure reduction is also greatly reduced, at which time and under which circumstances it will be stored and shipped. f

I propose to use refrigerating machinery including compressor, condenser, receiver and evaporator elements, by cascading where the evaporator of one refrigerant cools the condenser of the second refrigerant in a similar refrigerating circuit and the second refrigerant cools the methane in the evaporator of the methane circuit. In the first two circuits the refrigerant is recirculated or recycled through the system. In the third circuit the compressor and condenser will produce the liquefied methane at ap-.

proximately -1l5.8 degrees F. and at approximately 675 pounds absolute.

The liquid methane will then be discharged into an insulated portable receiver, will be allowed there to expand to atmospheric pressure with resultant sharp temperature drop of the liquid. This reduction in pressure will allow some of the gas to evaporate and will cool the remainder. The liquid will remain in the receiver. The evaporated gas will be returned to the system for further compression and liquefaction, the liquid left in the receiver being replaced by methane from the outside mixed with that which returns from the insulated receiver and this process will continue until a receiver of substantial size is substantially filled with liquefied methane at a temperature of approximately 258 degrees F. and .at a pressure of approximately atmospheric.

When the portable receiver is filled with the liquefied 2 methane, if it were possible to so insulate it that no heat would be added to it, the methane would remain liquid without boiling or evaporation at the temperature of the receiver. Actually, of course, no matter how well insulated the receiver is, some heat is added. Thatheat causes the liquid to boil orevaporate and so gas is given off from the surface of the. liquid. This gas, unless released,would soon raise the pressure in thereceiver far above the safety point so it must be allowed to escape.

Thus the pressure in the receiver remains at a substantially constant level and evaporation continues at a rate dependent upon the rate at which heat is added. The liquid remains at the same temperature just as water re mains at the same temperature while it boils. This gas may be 'used to assist in maintaining the temperature of the remaining liquefied gas constant so as to control the rate at which heat is allowed to reach the mass of liquefied gas, and may then be used as fuel or for any other purpose desired. w

, Inone instance, I-propose that the receiver be installed in 1a-boat or barge and the escaping gas will be used to furnish-the fuel to operate the engine to propel the ship to its destination, at which point the remaining liquefied gas will be disposed-of.

The transportation of such a gas as methane by pip line is an exceedingly expensive proposition because of the necessity of a continuous pipe from point of origin to point of use and the expense of building and operating a pipe line can only be justified when a continuous maximum volume of gas is to be transported. The method and apparatus which I propose which involves a com pressing and refrigerating system at pointof origin a peripatetic or wandering insulated receiver and a place to put the gas at the end of the line is therefore much less' expensive and much more flexible because the receiver may move to any desired point where the gas is needed. The cost of propelling the liquefied gas from point of origin to point of use in-terms of gas loss furnishing the power to operate the engine is so small that it is negligible and furnishes n0 bar to the operating of the flexible system I propose.

My invention is illustrated more or less diagrammatically in the accompanyingdrawing wherein is shown a diagrammatic ,flow sheet.

Like parts are indicated by like characters throughout the specification and drawing. 7 a

A is the first stage of refrigeration. It'includes compressor 1-, condenser 2, receiver 3, evaporator 4. B is the second stage of refrigeration. It includes a compressor 5, condenser 6, cooled by the evaporator 4 of stage A, a receiver 7 and an evaporator 8.

a C is the final stage of refrigeration wherein 9 is a supply pipe bringing methane to the compressor 10, which discharges into the condenser 11, cooled by the evaporator8 of the B stage, discharging liquefied gas through a pipe 12 to a receiver tank 13 on the ship 14 insulated at 15. 16 is a return pipe for evaporated gas from the receiver tank 13 to the low pressure side of the compressor 10.

When the receiver tank on the ship is filled, the pipes 12 and 16 to the tank are disconnected, the valves 17 being closed.- Then as the liquid methane in the receiver tank 13 evaporates, gas passes through the relief valve 18 to the pipe 19 to the engine 20 to drive the ship.

When the ship reaches its destination, pipe 19 is con nected to a pipe 21 on the shore and the methane under the residual pressure in the receiver 13 or the cold evaporated gas passes through the evaporator or heat exchanger 22 of a refrigerating system. Thereafter, the warm gas -is discharged through the pipe 23 to the burner 24 under the boiler 25.

The particular details of the evaporator and the burner 3 'I l a form no part of my invention and are not illustrated. The gas may be used under a boiler.v It might be stored in a receiver on shore. It might be used as fuel for internal combustion engines or it might be burned in other heat processes, as desired. The point'is that after the cold methane from the receiver on the boat has been used to extract heat from something else, the warmed gas may then be used to generate power or heat as the case may be.

Whether the engine uses all the evaporated gas or not to propel the boat, the evaporated gas must be permitted to escape from the receiver tank at such a rate that the pressure in the tank does not rise above a predetermined maximum so any excess of evaporated gas must be permitted to escape freely to the'atmosphere, at a pressure, but slightly above atmospheric, set by the relief valve 18 in the discharge pipe 26. So long as the engine uses gas at a rate not greater than the-evaporation rate, all the gas passes through the engine and is there burned. When the evaporation rate is higher than the engine use rate, the relief valve 18 permits gas to discharge through the pipe 26- from the engine supply pipe 19 to a mixing nozzle 27 where the methane is mixed with an inert: gaswhich reaches the nozzle through a pipe 28 from the inert gas reservoir 29. A control mechanism 30 automatically opens the supply pipe for the inert gas whenthe pressure in the line between the receiver and'th'e engine exceeds the safety point so that the inert gas is automatically mixed with hydrocarbon vapor when that is discharged to the atmosphere. Thus an inertor at least a non-explosive, non-poisonous mixture will be'dischargedto the atmosphere.

To avoid explosion the receiver in the boat must never be allowed to contain oxygen above a certain predetermined safety point. To guard against this, 31 indicates a gas analysis mechanism. This gas analysis mechanism is so adjusted that wheneverthe oxygen content in the receiver 13 exceeds the safety point, it opens the valve 32 in the pipe 33 leading from inert gas reservoir 29 so as to force inert gas into the receiver at a rate sufiicient to maintain the oxygen content percentage below the danger point. As the tank is being filled from the shore, such inert gas passes out with the gas returned to the compressor, being separated out by any suitable means 34 in the supply line to the compressor.

36 is a valve in the pipe 19 whereby the supply of gas to the engine may be shut off when the valve 35 is opened to permit gas to pass to the heat exchanger 22 through the flexible removable connecting pipe 21, the valve 35, of course, being closed when the boat is on the way to the point of use. i

I have illustrated at A, B and C a suitable arrangement for the compression and cooling of the gas which 1 propose to store and ship. Under some circumstances the natural pressure of the gas as it isdischarged fromthe well may obviate the necessity of using at least the compressor in the final stage. It is Well-known that under some circumstances the gas pressures are exceedingly high as the well discharges and therefore under such circumstances this pressure may be taken advantage of in the liquefaction of the gas.

The use and operation of my invention are as follows:

The use and operation of this invention is in a very real sense the same as the use of any cascading low temperature refrigerating system. The first two stages would be, for instance, in Louisiana, near the mouth of the Mississippi River. Part of the third stage would be there, namely, the compressor and the condenser. The receiver is Wandering or peripatetic. That is, it is the tank in the boat that moves back and forth between New Orleans and Chicago. The evaporator is in Chicago. The third stage differs from the usual. in that the refrigerant, the gas which is compressed and liquefied never returns again to the system but it is replaced by other similar gas at the southern end of. the line.

In a sense, a part of the third stage can be said to be located entirely in Louisiana, that is to say, as the liquid methane is supplied to the receiver vessel on the ship, while most of the liquid stays there, some of it evaporates and is returned to the compressor for recirculation with additional gas added :to the system to replace that which remains as liquid in the receiver vessel.

The rate at which the liquid evaporates, depending as it does upon the amount of heat supplied to the liquid mass, varies with the outside temperature. The'rate at which the propelling mechanism uses thisgas varies from zero when. the power mechanism on the boatis; at rest to a maximum. The evaporator rate may well be such as to supply more than enough fuel toop'erate the propelling engine and in any event, under circumstances when the engine is at rest or developing low power, the rate of evaporation-will be greater than the rate of use, therefore the importance of the control which permits wasting to atmosphere of excess gas to avoid building up dangerous pressures in the peripatetic receiver.

1 claim:

1. The method of storing hydrocarbons of low boiling point, consisting essentially of methane, which consists in providing a supply of hydrocarbon in gaseous condition, compressing it to a pressure above its critical pressure, cooling the compressed ga to a temperature above liquefaction temperature under the pressure condition'existing, then discharging it to a storage receiver with expansion to about atmospheric pressure to lower the temperature to liquefaction temperature to produce a mixture of liquid and gas, withdrawing the gaseous phase as a gas and adding gas from the supply and recompressing and recooling it and then sending it back to the receiver, continuing such circulation until the receiver is filled with a suitable quantity of. liquid at Substantially atmospheric pressure, bleeding the vapors released from the liquid in the receiver when the pressure in the receiver exceeds a predetermined level thereby to maintain a pressure therein at substantially atmospheric pressure.

2. The method of storing hydrocarbons of low boiling point, consisting essentially of methane, which consists in providing a supply of the hydrocarbon in gaseous condition at a pressure above its critical pressure, cooling the compressed gas to a temperature above liquefaction temperature under the pressure conditions existing, then discharging it to astorage receiver with expansion to about atmospheric pressure to lower the temperature to liquefaction temperature to produce a mixture of liquid and gas, withdrawing the gaseous phase as a gas and recompressing the gas for addition to the supply followed by recoolingand then sending it back to the receiver, continuing such. circulation until the receiver is filled with a suitable quantity of liquid at substantially atmospheric pressure, bleeding the'vapors released from the liquid in the receiver when the pressure in the receiver exceeds a predetermined level thereby to maintain a pressure therein at substantially atmospheric pressure.

References Cited in the file of this patent UNITED STATES PATENTS Thompson May 1, 1951 

1. THE METHOD OF STROING HYDROCARBONS OF LOW BOILING POINT, CONSISTING ESSENTIALLY OF METHANE, WHICH CONSISTS IN PROVIDING A SUPPLY OF HYDROCARBON IN GASEOUS CONDITION, COMPRESSING IT TO A PRESSURE ABOVE ITS CRITICAL PRESSURE, COOLING THE COMPRESSED GAS TO A TEMPERATURE ABOVE LIQUEFACTION TEMPERATURE UNDER THE PRESSURE CONDITION EXISTING, THEN DISCHARGING IT TO A STORAGE RECEIVER WITH EXPANSION TO ABOUT ATMOSPHERIC PRESSURE TO LOWER THE TEMPERATURE TO LIQUEFACTION TEMPERATURE TO PRODUCE A MIXTURE OF LIQUID AND GAS, WITHDRAWING THE GASEOUS PHASE AS A GAS AND ADDING GAS FROM THE SUPPLY AND RECOMPRESSING AND RECOOLING IT AND THEN SENDING IT BACK TO THE RECEIVER, CONTINUING SUCH CIRCULATION UNTIL THE RECEIVER IS FILLED WITH A SUITABLE QUANTITY OF LIQUID AT SUBSTANTIALLY ATMOSPHERIC PRESSURE, BLEEDING THE VAPORS RELEASED FROM THE LIQUID IN THE RECEIVER WHEN THE PRESSURE IN THE RECEIVER EXCEEDS A PREDETERMINED LEVEL THEREBY TO MAINTAIN A PRESSURE THEREIN AT SUBSTANTIALLY ATMOSPHERIC PRESSURE. 